The Beckman spectrophotometer Model DU has proved to be a useful instrument for measuring spectral directional reflectance. Like other spectrophotometers it is subject to slit-width and stray-energy errors. The magnitude of these errors and techniques for minimizing them are discussed. The viewing geometry and an adaptor for four-inch square specimens are described.
H. K. HAMMOND III and I. NIMEROFF, "Minimizing Anomalies in Reflectance Measurements with the Beckman Quartz Spectrophotometer," J. Opt. Soc. Am. 42, 367-372 (1952)